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CHAPTER 4 PORT FUNCTIONS
(2) Pull-up resistor option register (PUOH, PUOL)
This register is used to set whether to use an internal pull-up resistor at each port or not. A pull-up resistor
is internally used at bits which are set to the input mode at a port where on-chip pull-up resistor use has been
specified with PUOH, PUOL. No on-chip pull-up resistors can be used to the bits set to the output mode or
to the bits used as an analog input pin, irrespective of PUOH or PUOL setting.
PUOH and PUOL are set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets this register to 00H.
Cautions 1. P00 pin does not incorporate a pull-up resistor.
2. When port 1 is used as dual-function pin, an on-chip pull-up resistor cannot be used even
if 1 is set in PUOL bit 1 (PUO1).
Figure 4-11. Pull-Up Resistor Option Register Format
Caution Set 0 to the bits 0, 1, 3 to 7 of PUOH and bits 2, 4, 6 of PUOL.
PUO7 0 PUO5 0 0 PUO1 PUO0PUOL
PUOm
Pm Internal Pull-up Resistor Selection
(m = 0, 1, 3, 5, 7, 10)
0
1
Internal pull-up resistor not used
Internal pull-up resistor used
FFF7H 00H R/W
7654
PUO3
76 32 0
1
00
0 0 PUO10
00PUOH FFF3H 00H R/W
7654Symbol
Address
After
Reset
R/W
0
76 32 0
1